1. Field Of The Invention
This invention relates to an injector apparatus having endless gripper chains and endless roller chains for inserting and removing coiled tubing into and out of subterranean wellbores such as those used in the production of oil and gas. More particularly, the disclosed invention relates to coiled tubing injectors having the ability to easily and quickly accommodate the passage of tools and wellhead equipment having large nominal diameters through the injector while the injector remains installed about the wellhead.
2. Description Of The Prior Art
After a well has been completed to produce oil or gas, it is necessary to periodically service the well. There are many occasions where the service procedure is carried out using coiled tubing. Such tubing is inserted into the wellhead through a lubricator assembly or stuffing box. Typically, this is necessary because there is a pressure differential at the surface of the well and the atmosphere, which may have been naturally or artificially created, that serves to produce oil or gas or a mixture thereof from the pressurized well. The tubing that is inserted into the well is normally inserted through a lubricator mechanism which provides a seal about the O.D. of the tubing for the retention of any pressure that may be present at or near the surface of the well. The tubing is inserted by an injector which generally incorporates a tubing guide, or gooseneck, and a multitude of gripper blocks for handling the tubing as it passes through the injector. The tubing is relatively flexible and can therefore be cyclically coiled onto and off of a spool, or reel, by the injector which often acts in concert with a windlass and a power supply which drives the spool, or reel. One such exemplary injector is the Otis Reeled Tubing Injector. The injector utilizes a pair of opposed endless drive chains which are arranged in a common plane. These opposed endless drive chains are often referred to as gripper chains because each chain has a multitude of gripper blocks attached therealong. The gripper chains are driven by respective drive sprockets which are in turn powered by a reversible hydraulic motor. Each gripper chain is also provided with a respective idler sprocket to maintain each gripper chain within the common plane. Both the drive sprockets and idler sprockets are mounted on a common frame wherein the distance between the centers of all the sprockets are essentially of a constant distance from each other. That is the drive sprockets are free to rotate but are not free to move either vertically or laterally with respect to each other and the idler sprockets are not free to move laterally with respect to each other, but are vertically adjustable within a limited amount in order to set the amount of play in each gripper chain. Such vertical adjustment is done by either a mechanical adjusting means or a hydraulic adjusting means. Typically, the adjustment is made when the injector is not in operation.
The opposed gripper chains, preferably via the gripper blocks, sequentially grasp the coiled tubing that is positioned between the opposed gripper chains. When the gripper chains are in motion, each chain has a gripper block that is coming into contact with the coiled tubing as another gripper block on the same gripper chain is breaking contact with the coiled tubing. This continues in an endless fashion as the gripper chains are driven to force the tubing into or out of the wellbore, depending on the direction in which the drive sprockets are rotated. Preferably, gripper blocks such as those set forth in U.S. Pat. No. 5,094,340, issued Mar. 10, 1992 to Avakov, which is incorporated herein, are used.
Because the gripper chain drive sprockets and idler sprockets are essentially in a fixed relationship with each other, the gripper chain is provided with a predetermined amount of slack which allows the gripper chain to be biased against the coiled tubing to inject the tubing into and out of the wellbore. This biasing is accomplished with a endless roller chain disposed inside each gripper chain, and each roller chain being driven by sprockets rotatably mounted on a respective linear bearing beam. A linkage and hydraulic cylinder mechanism allows the linear bearing beams to be moved toward one another so that each roller chain is moved against its corresponding gripper chain such that the tubing facing portion of gripper chain is moved toward the tubing so that the gripper blocks can engage the tubing and move it through the apparatus.
The fixed distance between each set of gripper chain drives and idler sprockets requires some significant lateral movement in the gripper chain when engaged by the roller chain on the corresponding linear beam in order to allow the gripper chains to engage the tubing by way of the gripper blocks. The reason for having the requisite amount of lateral play in the gripper chains is to provide a limited amount of clearance between the gripper chains, upon moving the respective roller chains away from the vertical center line of the injector, to allow the passage of tubing and tools having larger outside diameters or dimensions. An inherent shortcoming in this design is that the required slack can often cause misalignment problems and even binding problems with the chains due to having to accommodate ever increasing outside nominal dimensions of downhole tools and wellhead equipment. Another troublesome characteristic manifests itself in the large approach and departure angles de:fined by the region where the respective paths of the gripper chains converge upon, and diverge away from, the working center line of the injector wherein the coiled tubing is preferably positioned for being injected or extracted into or out of the well. The large approach and departure angles reduce the overall efficiency of the injector by causing increased friction due to the longer chains that must be used and the necessity of supporting and contending with the reactive forces generated by the chains when the injector is in operation.
A further, if not more predominate reason why large gripper chain approach and departure angles are not desired, is that large angles tend to increase the likelihood of the chain-mounted gripper blocks to mark, or gouge, the tubing as the blocks come into contact with the tubing. Such marks, or gouges, create stress risers within the wall of the tubing which can lead to premature structural failure of the tubing. Therefore, a tubing injector apparatus not having large gripper chain approach or departure angles, yet being able to accommodate large diameter tubing and wellhead equipment would advance the art considerably.
Therefore there is a need within the art to provide an injector that, while the injector remains installed about the wellhead, can accommodate large nominal diameter tools and surface equipment, yet can provide efficient and reliable chain operation to generate the high forces needed for injecting and extracting tubing of long lengths and large diameters into and out of the wellbore.
Another need within the art is for an injector having the ability to accommodate a wide range of tubing diameters while in operation. Such an injector would allow for improving operations wherein coiled tubing having differing diameters that have been connected to each other to form a single string of tubing are being used in the servicing of the well.
Another need within the art is for an injector that can accommodate the ever increasing nominal outside diameters of tubing while avoiding: chain mis-alignment, chain binding tendencies, improper chain tension, increased chain friction caused by excessively long gripper chains, gripper block marking or gouging, and other inherent design problems of prior injectors which manifest themselves when working with tubing, tools, and surface equipment having large nominal outside diameters.
These and other needs are fulfilled by the present invention of the injector apparatus disclosed herein.